Inverter and converter bridges have one or more legs with two complementary switches which can never be permitted to simultaneously be in the "ON" state. Because the switches are not ideal and therefore have "turn ON" and "turn OFF" delays, an intentional dead-time between the "turn OFF" signal of one switch and the "turn ON" signal of the complementary switch must be inserted in order to avoid a short circuit of the power supply. In other words, the turn-on of the complementary switch in the inverter leg (or converter leg) is delayed by a dead-time .DELTA.T. The duration of the dead-time .DELTA.T must be sufficient to ensure that a switch in the inverter/converter leg is off before allowing the complementary switch in the bridge leg to turn on. The dead-time .DELTA.T is also known as a blanking interval.
Dead-time effectively creates a voltage disturbance which acts on the current regulators in current controlled inverters and converters. The sign of the voltage disturbance depends on the sign of the load current. This disturbance changes sign at every zero crossing of the load current. It is in the form of voltage steps ideally, that is, when infinite load inductances are assumed. The amplitude of the step depends on the dead-time. It is equal to 2.times.V.sub.bus .times.(.DELTA.T/TPWM) where V.sub.bus is the DC bus voltage, .DELTA.T is the total dead-time and TPWM is the PWM cycle time. For bipolar transistors the total dead-time can be as high as 15% of the PWM cycle time.